Hi,
I am writing simple Linux module mod.c.
When I compile mod.c file, it creates two output file **mod.o** and **mod.ko**.
So I just want to know,
What is the difference between mod.o and mod.ko file?

mod.ko files are used as kernel modules.

These files are used whenever necessary .For example in early days of linux everything was prebuild in a kernel .
This made kernel heavy and bit slow.

The new approach made kernel bit fast and responsive, all due to modularizing the kernel.
In this approach functionality is loaded to memory whenever it is required (this make lot of sense )
.
For e.g
You will only need a Bluetooth drivers loaded in memory whenever you plug in a bluetooth device.
So having Bluetooth drivers loaded in memory for all the time makes no sense.
Such modules are stored with .ko extension.